Audio modulation system



Sept. 1, 1964 W. C. WAYNE, JR

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IN V EN TOR.

WILLIAM C.WAYNE,JZ.

BY MJZJM N- llwfm d ATTORNEY-5 United States Patent Filed July 27, 1960, Set. No. 45,609 15 Claims. (Cl. 84-1.24)

-. This application is a continuation-in-part of my application Serial No. 631,650, filed December 31, 1956, now Patent No. 3,004,460, and entitled Audio Modulation System.

The present invention relates generally to systems for achieving an ensemble effect in music by processing a band of audio frequencies, and more particularly by translating the frequency spectrum so that it is either sharp or flat in controllable degree, over its entire extent, or is in part flat and in part sharp. The translated frequency spectrum may be combined with a corresponding untranslated frequency spectrum acoustically, as by transducing the translated and untranslated spectra in, preferably spaced, separated, loudspeaker systems.

The traditional pipe organ consists of many ranks of pipes which are invariably out of tune. Certain ranks of pipes, referred to as celestes, are purposely detuned by a considerable amount to produce a rich ensemble effect in the composite tone, which is especially desirable for use in ecclesiastical music.

Inmy prior application, above referred to, I provided a system for electrically processing a musical fre quency spectrum, from whatever source derived, so as to achieve a processed frequency spectrum which is capable of simulating the ensemble effect of pipe organs, and more particularly the celeste effect, and which is in fact more flexible in respect to the variety of ensemble effects made available than is the traditional pipe organ.

In my prior application, I disclosed utilization of a plurality of wide band, single side band modulators, each of which continually shifts the phase of a wide band audio spectrum, deriving preferably from a musical instrument, in such sense as to produce a continuously changing phase shift of the entire spectrum in a given direction, which is equivalent to a frequency shift of the entire spectrum in a given sense, i.e., either fiat or sharp. Different octaves of the wide band spectrum are selected from the wide band outputs of theseveral modulators by means of band pass filters, and the filtered sub-bands are then recombined to provide a processed wide band frequency spectrum. The latter may be thus translated in frequency over its entire range, either flat or sharp, or in part flat and in .part sharp, and in controllable extent, as desired.

The processed and unprocessed tones may be acoustically transduced by a single transducer or by adjacent transducers. Alternatively, the unprocessed frequency spectrum may be fed to one loudspeaker system, and the processed frequency spectrum to a second loudspeaker widely spaced from the first, in order to achieve maximum spatial effect. This effect is especially appreciated when heard binaurally and corresponds to an apparent tonal movement as well as an increase in the tonal source size, thus greatly enhancing the musical interest of the program material.

- 3,147,333 Patented Sept. 1, 1964 quency deviation, and the selected sub-bands may be additively combined to form a processed audio frequency band. Since the algebraic sign of the frequency shift, positive or negative, corresponds with the relative phase sequences of signals supplied to a single side band modulator in the modulation process, the sub-bands may have frequency deviations of either algebraic sign at will, i.e., any side band may be either flat or sharp. For some purposes it is desirable to derive sub-bands adjacent ones of which are frequency shifted in opposite senses. It

' may also be preferred that sub-bands be of octaval widths,

Since it is desired to maintain the frequency shift correspondnig with any continuing phase variation at a selected substantially constant precentage over a relatively wide frequency band, frequency shift of the entire audio band is accomplished in separate channels or separate sub-bands of the audio spectrum and the modulation frequency or the frequency shift separately selected for each channel as a substantially fixed percentage of the center frequency of the channel. Sub-bands may then be selected, from the several frequency shifted bands, which have the desired values of percentage frerather than equal widths on a per cycle basis, so that notes of corresponding nomenclature and adjacent in the musical scale shall not be frequency shifted identically, i.e., shall be shifted either different amounts in the same sense, or shall be shifted in opposite senses.

Since the separate sub-bands are derived by means of band pass filters having overlapping frequency characteristics, it inevitably occurs that some frequencies will pass through two adjacent filters. For example, assuming all the channels to be raised in frequency, and assuming that the center frequencies of the channels are 375 c.p.s, 750 c.p.s, 1,500 c.p.s, and 3,000 c.p.s., a 375 c.p.s input may be raised in frequency 1 c.p.s., yielding an output from the modulator of 376 c.p.s. A 750 c.p.s input signal may be raised two c.p.s, giving an output of 752 c.p.s. An input frequency mid-way between these two frequencies, i.e., about 530 c.p.s., then yields 531 c.p.s. from the first channel and 532 c.p.s. from the second channel. In accordance with my prior invention these signals are electrically added and produce beats in the usual manner having a subjective beat rate of 532 minus 531, equal to 1 c.p.s. The same analysis may be provided for all the channels, so that the invention as disclosed in the above identified application inherently produces subjective very low frequency beats.

In accordance with the present invention I combine various modulator output channels acoustically instead of electrically. Each channel may drive its own speaker, which is preferably located some distance apart in the listening room from the speakers pertaining to the other channels. It then becomes feasible to utilize a relatively small speaker for each channel, and also to utilize relatively inexpensive power amplifiers for each channel, since each channel covers an essentially very narrow band. It may also be expected that as a result of separating the wide audio band emanating from an electrical musical instrument into bands which are essentially an octave in width, intermodulation distortion may be redeuced substantially. Enchanced musical effects may then be provided by virtue of the spatial separation of the loudspeakers and the subjective low frequency beats are significantly reduced because acoustical addition and binaural audition are employed.

In accordance with a first embodiment of the invention, the output of an electronic organ, or other source of musical spectrum, may be applied to four modulatorchannels, each of which is one octave wide. The first channel may introduce a rise in frequency, the second a drop in frequency, the third a rise in frequency, and the fourth a drop in frequency, i.e., alternate channels may be sharp and flat respectively. The first and third channels may then supply a first speaker while the second and fourth channels supply a second speaker, the speakers being spatially separated. It then follows that each single speaker is presented with no tones which are adjacent in frequency, so that the output of any speaker will not contain material capable of generating low frequency beat patterns caused by reinforcements and cancellations of signals having nearly the same frequencies. In accordance with a modification of the invention, the first two channels, i.e., the two lowest channels, may both be sharp and the two highest channels may both be fiat.

In accordance with a third modification of the invention, all the tone modulators may introduce a frequency shift in the same sense, i.e., either flat or sharp, but the shifts may be of different extents in the separate channels. The outputs of the separate channels may be supplied to spatially separated speakers.

In accordance with still another embodiment of the invention, two modulator systems may be utilized, one of which may provide four sub-bands all of which are frequency shifted upwardly while the other may provide four sub-bands all of which are frequency shifted downwardly. The sharp shift may be relatively small and the flat shift relatively large, if desired. On the assumption that each modulation system provides four subbands or channels in order of center frequencies of the bands, each of which is one octave in width, two speaker outputs may be utilized for each modulation system, to one of which may be supplied a first and third sub-band and to the other of which may be supplied a second and fourth sub-band deriving from each modulation system. The twomodulation systems thus provide four outputs. One of the outputs is constituted of a first and third band, slightly sharp, the other is constituted of a second and fourth sub-band slightly sharp, the third is constituted of a first and third sub-band considerably fiat and the fourth is constituted of a second and fourth sub-band considerably flat. Two speakers may be utilized, to one of which is supplied the first and fourth tonal components, while to the other is supplied the second and third of the tonal components. By virtue of the principles hereinabove explained, avoidance of electrical addition of nearly the same frequencies is achieved.

In connection with each of the above briefly described modifications of the present invention, the original unprocessed tone may be acoustically transduced into the same space as the processed tone, the present invention concerning itself primarily with the elimination of low frequency beats, by avoidance of electrical addition of tones of adjacent frequencies in systems of the type de scribed and claimed in the above identified application.

It is an object of the invention to provide a system for shifting the frequencies of a wide audio spectrum representing music, each of the frequencies being shifted by approximately the same percentage deviation, by dividing the frequency spectrum into adjacent sub-bands, passing the sub-bands through separate channels involving different frequency shifts, and acoustically reproducing the signals in the separate channels without electrical addition of adjacent frequencies which pass simultaneously through two channels.

Another object of the invention resides in the provision of a system for achieving an ensemble effect by converting components of an audio spectrum to relatively displaced frequency positions and separately acoustically reproducing frequencies which have been differently displaced.

Still another object of the invention resides in the provision of a system for separately processing adjacent octaves of a musical spectrum and acoustically reproducing the separate octaves by means of separate transducers. 7

Still another object of the invention resides in the provision of a system for processing a musical spectrum by separately processing different sub-bands of the spectrum, and acoustically reproducing the separate sub-bands in such manner that no single transducer will reproduce two subbands having adjacent frequencies.

It is another object of the invention to provide a system for processing a first musical spectrum upwardly in frequency, and a second related musical spectrum downwardly in frequency, and acoustically radiating frequency components deriving from both processing mechanisms,

in such manner that adjacent frequencies are never electrically combined.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following description of several embodiments thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a first modification of the present invention, illustrated in block diagram;

FIGURE 2 is a block diagram of a modification of the system of FIGURE 1;

FIGURE 3 is a block diagram of a further modification of the systems of FIGURES 1 and 2, employing a single processing system; and

FIGURE 4 is still another modification of the invention illustrated in block diagram, employing two tone processing systems.

Referring now more specifically to FIGURE 1 of the accompanying drawings, the reference numeral 10 denotes a source of a musical spectrum, such as an electronic organ. The invention is intended primarily for application to electronic organs, but may be employed in processing musical spectra deriving from motion picture sound tracks, magnetic tape reproducers, microphones, and the like. The output spectrum deriving from the electronic organ, and constituting the entire tonal output of that organ at any given instant, may be reproduced into a given space, or listening area, over a channel 11, containing an amplifier 12 and a speaker 13 in cascade. In addition, the spectrum may be supplied over a wide-band 120 phase shiftingg network 14, included in a tone processing unit 15, of the type disclosed in detail in my prior application for U.S. patent, above identified. The processing unit 15 includes, in the present specific embodiment of my invention, four frequency shift channels in parallel, denoted by the reference numerals 16, 17, 18 and 19, each of which includes a frequency shift tone modulator which has the function of varying in a single direction all the frequencies of the audio spectrum applied thereto. Suitable circuitry for accomplishing this result is described and illustrated in the above identified application.

In the system of FIGURE 1, the channel 16 includes a tone modulator 20, which raises the frequency of the spectrum applied thereto 1 c.p.s. The channel 17, on the other hand, includes a tone modulator 21, which raises all the frequencies of the spectrum applied thereto by approximately 2 c.p.s. The channel 18 includes a tone modulator 22, providing a reduction of frequencies of the spectrum applied thereto, by a factor of four c.p.s. while the channel 197includes a modulator 23 which effects a reduction of approximately eight c.p.s. In cascade with the tone modulator 20 is a band pass filter 24, centered on 375 c.p.s., and having a band pass adequate to pass one octave. In cascade with the tone modulator 21 is a band pass filter 25 having a center frequency of 750 c.p.s. and a band width of one octave. In cascade with the tone modulator 23 is a band pass filter 26 having a center frequency of 1,500 c.p.s. and a band width of one octave, while in cascade with the tone modulator 23 is a band pass filter 27 having a center frequency of 3,000 c.p.s. and a band pass of one octave. The band pass filters 24, 25, 26 and 27 have overlaps of their characteristics, i.e., it is not possible to build band pass filters having infinitely sharp cut off, and in the present application, this is not desirable and it may be preferable to utilize band pass filters having gently sloping sides. Were the outputs of the band pass filters 24, 25, 26 and 27, or any two adjacent ones of these, applied to an additive network for electrical addi tion, prior to application to a speaker or other acoustical transducer, nominally the same freqencies would pass through the filters 24, 25, due to the overlap of their pass bands. For example, shifted frequencies of 531 c.p.s. and 532 c.p.s., would pass through the skirts of both the filters 24 and 25. In this condition there would be a difvmerals 52, 53, 54 and 55.

. ference of 1 c.p.s. between these frequencies (which Were identical in the input channels 16, 17, namely 530 c.p.s.), and this difference of 1 c.p.s. could produce a marked beat pattern apparent to a listener, which is undesirable. In accordance with the present invention, the outputs of the band pass filters 25and 27 are additively combined and'applied via an amplifier 30 to a speaker 31. The outputs of the band pass filters 24 and 26 are separately additively combined and applied via an amplifier 32 to a speaker 33. Accordingly, neither speaker 31 nor speaker 33 includes any frequencies which have been shifted by slightly different amounts, so as to give rise to low frequency beats. The speakers 31 and 33 may be spatially separated further to avoid the generation of low frequency beats and to add to the musical interest of the acoustically transmitted tones.

The system, of FIGURE 2 is generally similar to the system of FIGURE 1 and corresponding elements in the two systems have accordingly been identified by identical numerals of reference, and are not further described.

The system of FIGURE 2 differs from the system of FIGURE 1 in that the tone modulator 21 of FIGURE 1 has been replaced by a tone modulator 21' which effects a reduction of frequencies of approximately 2 c.p.s. in place of an increase, and the tone modulator 22 of FIG- URE 1 has been replaced by a tone modulator 22 which effects an increase of frequencies instead of a decrease. The neteifect, then, in the system of FIGURE 2, is that speaker 33transmits only tones which have been rendered sharp and the speaker 31 only tones which have been rendered flat while in the system of FIGURE 1 the speaker 33 transmits tones which have been in part rendered sharp and in part rendered fiat, while the speaker 31 transmits, in the system of FIGURE 1, tones which have been in part rendered sharp and in part rendered flat. Musical interest in the two cases is different, because of the effect upon the overtones contained in the spectrum. In the system of FIGURE 2, some overtones which were originally harmonically related becomes slightly different in frequency but both in the same sense, whereas in the system of FIGURE 1 they not only become slightly different, but one is sharp while the other is flat, depending upon which of the band pass filters the overtones pass through. So, in the system of FIGURE 1 a tone having a fundamental adjacent to 375 cycles and having a fourth harmonic, the fundamental is raised by l c.p.s. and the fourth harmonic decreased by 4 c.p.s., whereas in the system of FIGURE 2 that same note would have its fundamental raised by 1 c.p.s. and itsfourth harmonic raised by 4 c.p.s.

In the system of FIGURE 3, which represents a modification of the systems of FIGURES 1 and 2, components identical with those employed in the system of FIGURES l and 2 are identified by the same numerals of reference.

In the system of FIGURE 3 the tone modulators 20 to 23 of FIGURE 1 are identified by the reference numerals 20a to 20d to indicate that these tone modulators may provide different frequencies changes than was the case in the system of FIGURE 1. More specifically, it is preferred in the system of FIGURE 3 that all the modulators provide either an increase or a decrease of frequency, although this is not essential to the system, and in fact certain of the modulators may provide sharp and the others flat effects, if desired, particularly if it is found that in a given electronic organ or musical instrument interesting musical effects are thereby produced. The outputs of the band pass filters 24, 25, 26 and 27 are supplied, respectively, to separate amplifiers 40, 41, 42 and 43, which in turn supply separate speakers 44, 45, 47 and 46. If desired, each of the band pass filters 24, 25, 26 and 27 may supply an additional speaker, via an additional amplifier, the latter being then identified by the reference numerals 48, 49, 50 and 51 and the speakers by the reference nu- In such case, the several speakers 13, 44 to 47 and 52 to 55 maybe distributed in a listening area, as may be experimentally determined, to provide the best and most interesting musical effects.

In the system of FIGURE 4 the two manuals of a two manual organ are separately treated, being derived on buses 60 and 61, respectively, and more specifically the swell manual supplies an audio spectrum to the bus 60 and the great manual to the bus 61. In cascade with the bus 60 is a tone processing system 151;, which is generically similar to that denominated 15a in the system of FIGURE 3, but in which the tones are all processed in a sharp direction. In cascade with the bus 61 is a similar tone process system 150 in which the tones are processed all flat. Each of the tone processing systems 15b and 150 includes four tone modulators and four filters, as in the system of FIGURE 3, the outputs of the filters appearing at the output of the system 15b on leads 62, 63, 64 and 65, in frequency bands centered on the frequencies 375 c.p.s., 750 c.p.s., 1,500 c.p.s., and 3,000 c.p.s., respectively. correspondingly, the outputs of the tone process system 15c appear on leads 66, 67, 68 and 63, respectively, in frequency bands centered on the frequencies 375 c.p.s., 750 c.p.s., 1,500 c.p.s. and 3,000 c.p.s., respectively. Where the swell manual provides string tones and the great manual provides flute tones, it will be found advantageous to provide a relatively small sharp displacement of frequencies, and a relatively large flat displacement of frequencies respectively, i.e., the frequency displacements are preferably not the same for both manuals.

In cascade with each of the output leads 62 to 69, inclusive, is inserted an isolating resistance 70, of about 20K. Following the isolating resistance 70, the channel 63 is interconnected with the channel 65 across a load resistance 71, and the channel 62 with the channel 64 across the load resistance 72. This corresponds with electrical addition of the outputs of channel 63, 65, and with electrical addition of the channels 62 and 64, but these pairs of channels do not include adjacent frequencies, so that no low frequency beats are generated by such addition. Similarly, the leads 66 and 68 are connected through their isolating resistances 70 to a load resistance 73, and the leads 67 and 69 through a common load 74. This corresponds with addition of total outputs of the channels 66, 68 and 67, 69 respectively, which is not deleterious, however, since these pairs of channels do not include or carry adjacent frequencies which might form very low frequency beats, Signal appearing across the resistance 71 is amplified in a voltage amplifier 75, and applied via a further isolating resistance 76 to a power amplifier 82 and speaker 82. Similarly, the output of channels 66 and 68 as they appear across resistance 73 are applied through a voltage amplifier 78 and an isolating resistance 79 to the input of the same power amplifier 82 and speaker 82'.

The outputs of the channels 62 and 64 as they appear across the resistance 72 are applied via a voltage amplifier 80 and an isolating resistance 81 to a power amplifier 77 and speaker 77', while the outputs of the channels 67 and '69 as they appear across the resistance 71 are amplified in a voltage amplifier 83 and applied via an isolating resistance 84 to the same power amplifier 77 and speaker 77.

Identifying the channels deriving from the tone processing units as #1, #2, #3 and #4, in the order of ascending mid-frequencies, channels #1 and #3 are applied to speaker 77 as they derive from tone processing system 15b, and accordingly few adjacent frequencies appear in the output of this speaker. Correspondingly, the outputs of channels #2 and #4, as they derive from tone process system 150, are applied to speaker 77' and again few adjacent, frequencies appear in the output of the speaker. Similarly, the speaker 82' carries channels #1 and #3 deriving from tone process system 150, and channels #2 and #4 deriving from tone process system 15b. Ac-

cordingly, each of the speakers 77' and 82' carries a full spectrum of audio sounds, but few audio frequencies which have passed through two adjacent filters of a given tone process system. 7

While I have described and illustrated several specific embodiments of my invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

What I claim is:

1. A system for generating chorus effects in music, comprising a source of at least one audio spectrum representing music, first means connected to said source for generating a plurality of sub-bands of audio frequencies substantially including all the frequencies of said audio frequency spectrum displaced in frequency by fixed amounts, and second means connected to said first means for separately acoustically transducing and radiating each of said sub-bands of audio frequency, said means for separately acoustically transducing and radiating consisting of plural space separated acoustic transducers.

2. A system for generating chorus effects in music, comprising a source of at least one audio spectrum representing music, a plurality of modulators for deriving from said at least one audio spectrum a plurality of frequency displaced audio spectra, the displacements being subaudio and different for each of said frequency displaced audio spectra and of substantially invariable values, a band-pass filter in cascade with each of said modulators, said filters having pass characteristics overlapping in pairs and overlapping only adjacent their cut-off regions, and means for only acoustically combining the outputs of at least those of said filters having overlapping cut-off regions.

3. The combination according to claim 2 wherein is included four modulators and four band pass filters each in cascade with one of said four modulators, said band pass filters having center frequencies of approximately F, 2F, 3F and 4F, said means for only acoustically combining the outputs of said filters including a first device for electrically combining only the outputs of the filters having center frequencies F and 3F, a second'device for electrically combining only the outputs of the filters having center frequencies 2F and 4F, and means for separately acoustically transducing the products of said first and second devices.

4. The combination according to claim 2 wherein said last means is a means for only acoustically combining the outputs of all said filters.

5. The combination according to claim 2 wherein the number of said plurality of frequency displaced audio spectra is four, and wherein the outputs of said first and third of said filters are combined electrically, wherein the outputs of said second and fourth of said filters are combined electrically, said filters being numbered in order of increasing center frequencies to pass bands of said band pass filters.

6. In a system for generating chorus effect in music, an electrical organ having a first manual, a second manual, said manuals arranged to generate wide band audio spectra, a first tone processing system connected in cas-' cade with said first manual for processing said first wide band audio spectrum, a second tone processing system connected in cascade with said second manual for processing said second wide band audio spectrum, said tone processing systems each including four output channels each carrying a processed audio sub-band of frequencies, said sub-bands of frequencies overlapping in part only and being ordered in respect to center frequencies, as

.first, second, third and fourth sub-bands, a first power amplifier, a first acoustic transducer connected in cascade with said first power amplifier, a second power amplifier, a second acoustic transducer in cascade with said second power amplifier, means for applying the firstand third sub-bands deriving from said first tone processing system and the second and fourth sub-bands deriving from said second tone processing system to said first power amplifier for amplification thereby, and means for applying the first and third sub-bands deriving from said second tone processing system and the second and fourth sub-bands deriving from said first tone processing system to said second power amplifier for amplification thereby.

7. The combination according to claim 6 wherein one of said tone processing systems is arranged to process tones fiat and the other of said tone processing systems is arranged to process tones sharp.

8. A system for generating chorus effect in music, comprising a source of an audio spectrum, means for shifting in a single direction only and by a first increment of frequency Ai all the frequencies of said audio spectrum to form a first processed audio'band, means for deriving from said first processed audio band a first frequency subband having a first upper frequency, means for shifting in a single direction only and by a second increment Af all the frequencies of said audio spectrum to form a second processed audio band, means for deriving from said second processed audio band a second frequency sub-band having a lowermost frequency below said first upper frequency and having also a second upper-frequency, means for shifting in a single direction only and by a third increment Af all the frequencies of said audio spectrum to form a third processed audio band, means for deriving from said third processed audio band a third frequency sub-band having a lowermost frequency below said second upper frequency, means for applying said second frequency sub-band in a first channel, a first acoustic transducer terminating said first channel, means for electrically combining said first and third sub-bands in a second channel, a second acoustic transducer terminating said second channel.

9. A system for generating chorus effect in music,

comprising a first source of a first audio spectrum representing music, a second source of a second audio spectrum representing music, first processing means in a first channel for processing said first audio spectrum by frequency shifting plural first sub-bands thereof each differently from the other, second processing means in a second channel for processing said second audio spectrum by shifting plural second sub-bands thereof each differently from the others, means for electrically combining all those first sub-bands selected from said first channel which lack immediately adjacent frequency boundaries into third and fourth channels, means electrically combining those of said second sub-bands selected from said second channel which lack immediately adjacent frequency boundaries into fifth and sixth channels, means electrically combining sub-bands from said third and fifth channels so as to provide in a seventh channel a filled audio frequency band deriving in substantially equal parts from said first audio spectrum and from said second audio spectrum, and means electrically combining all sub-bands excluded from said seventh channel into an eighth channel.

10. A system for generating chorus effects in music comprising a source of an audio spectrum representing music, said audio spectrum comprising an ordered array of adjacent sub-bands, means for modifying all said subbands in each of a plurality of channels, identically for each channel and differently among the channels, means for abstracting a different one of said sub-bands from each one of said channels, means for electrically combining only those of the abstracted sub-bands which contain no nominally identical frequencies into separate further channels, and a separate acoustic transducer in each of said separate further channels.

11. The combination according to claim 10 wherein said means for abstracting are band-pass filters, and Wherein'adjacent ones of said band-pass filters have overlapping frequency pass characteristics.

12. A system for generating chorus effect in music, comprising a source of first audio spectrum representing music, a source of a second audio spectrum representing music, each of said audio spectra comprising an array of four audio frequency sub-bands ordered in terms of values of mid-frequencies of the sub-bands, means for differently modulating the frequencies of all said subbands to provide first, second, third and fourth processed sub-bands deriving from said first audio spectrum and fifth, sixth, seventh and eighth processed sub-bands deriving from said second audio spectrum, the processed subbands retaining the orders of the first mentioned subbands, means for electrically combining the first, third, sixth and eighth sub-bands in a first channel and means for electrically combining the second, fourth, fifth and seventh sub-bands in a second channel.

13. The combination according to claim 12 wherein said means for differently modulating are means for frequency shifting in a single sense.

14. The combination according to claim 13 wherein said first four processed sub-bands are processed flat and wherein said second four processed sub-bands are References Cited in the file of this patent UNITED STATES PATENTS 2,261,268 Lovell Nov. 4, 1941 2,352,696 De Boer July 4, 1944 2,616,970 Broos Nov. 4, 1952 2,879,683 Martin Mar. 31, 1959 2,916,706 Timperman Dec. 8, 1959 3,004,460 Wayne Oct. 17, 1961 3,007,361 Wayne Nov. 7, 1961 

1. A SYSTEM FOR GENERATING CHORUS EFFECTS IN MUSIC, COMPRISING A SOURCE OF AT LEAST ONE AUDIO SPECTRUM REPRESENTING MUSIC, FIRST MEANS CONNECTED TO SAID SOURCE FOR GENERATING A PLURALITY OF SUB-BANDS OF AUDIO FREQUENCIES SUBSTANTIALLY INCLUDING ALL THE FREQUENCIES OF SAID AUDIO FREQUENCY SPECTRUM DISPLACED IN FREQUENCY BY FIXED AMOUNTS, AND SECOND MEANS CONNECTED TO SAID FIRST MEANS FOR SEPARATELY ACOUSTICALLY TRANSDUCING AND RADIATING EACH 